1. Field of the Invention
The present invention relates to a switching power supply and particularly relates to a technique for achieving higher efficiency and miniaturization of an insulating switching DC/DC converter.
2. Description of the Related Art
Conventionally switching power supply circuits using the Boost Half Bridge (BHB) method are proposed in which a booster circuit and a half bridge circuit are integrated (Reference 1, Reference 2, Reference 3, Reference 4). FIG. 29 shows a circuit configuration proposed in Reference 3. In FIG. 29, reference character E designates an input voltage source, reference numeral L1 designates an input choke coil, reference numeral L2 designates an output choke coil, reference numeral C0 designates an output smoothing capacitor, reference numeral R0 designates a load resistance, and reference numeral V0 designates an output DC voltage.
According to the circuit of the BHB method shown in FIG. 29, the input voltage source E is connected via the input choke coil L1 to the midpoint of two switching devices (FET1, FET2) having a half-bridge configuration, and the secondary winding current of a transformer T is subjected to full-wave rectification by two synchronous rectification MOSs (FET3, FET4). Further, the two switching devices (FET1, FET2) are controlled in a complementary manner.
According to Reference 4, a configuration for incorporating a booster choke into the primary winding of a transformer in the BHB method is proposed.
[Reference 1] Japanese Patent Application Publication No. 11-262263
[Reference 2] Haruo Watanabe and other two, “BHB (Boost Half Bridge) power supply,” Technical Report of IEICE, The Institute of Electronics, Information and Communication Engineers, EE98-17 (1998-07), pp. 28-34
[Reference 3] Haruo Watanabe, “High Efficiency On-board Power Supply using Boost Half Bridge Method,” Switching Power Supply System. Symposium 2000, Japan Management Association, B2-2
[Reference 4] Yoshiaki Matsuda, “Low Voltage Output High Efficiency DC/DC Converter,” Switching Power Supply System Symposium 2001, Japan Management Association, A2-3
However, in the circuit configurations having been conventionally proposed, although the output is reduced in ripple voltage and ripple current, the core of magnetic components (input choke coil, output choke coil, and transformer) is considerably increased in total DC bias magnetization, so that the core has a large volume and the overall apparatus has low efficiency.